Process for the recovery of rhenium and molybdenum values from molybdenite concentrate

ABSTRACT

PROCESS FOR THE RECOVERY OF MOLYBDENUM AND RHENIUM FROM MOLYBDENITE WHICH COMPRISES: OXIDIZING THE MOLYBDENUM IN THE MOLYBDENITE CONCENTRATE SLURRY TO THE HEXAVALENT FROM WITH OXYGEN OR OXYGEN-CONTAINING GASES AND LESS THAN A STOICHIOMETRIC AMOUNT OF NITRIC ACID FOR THE SULFIDE SULFUR PRESENT, RECOVERING MOLYBDENUM AND RHENIUM VALUES FROM THE RESULTING SOLUTION WHEN IT CONTAINS UP TO 600 G./L. OF SULFURIC ACID WITH AN AMINE OR QUATERNARY AMMONIUM TYPE EXTRACTANT, REMOVING THE MOLYBDENUM AND RHENIUM VALUES FROM THE EXTRANT WITH AMMONIUM HYDROXIDE, SELECTIVELY RECOVERING RHENIUM VALUES FROM THE ESULTING ALKALINE SOLUTION WITH A QUA TERNARY AMMONIUM TYPE EXTRACTANT, RECOVERING THE REMAINDER OF THE MOLYBDENUM VALUES FROM THE ELUATE, STRIPPING RHENIUM FROM THE EXTRACTANT WITH PERCHLORIC ACID OR POR PERCHLORATE SALT AND RECOVERING RHENIUM FROM THE STRIPPING SOLUTION.

June 12, 1973 E. w. DAUGHERTY ET AL 3,739,057

PROCESS FOR THE RECOVERY OF RHENIUM AND MOLYBDENUM VALUES FROM MOLYBDENITE CONCENTRATE Filed July 9, 1971 2 Sheets-Sheet 1 PROCESS FOR RECOVERY OF MOLYBDENUM AND RHENIUM VALUES FROM MOLYBDENITE CONCENTRATE MOLYBDENITE CONCENTRATE 0 H2O MOLYBDENITE HNO3 OXIDATION H O COUNTERCURRENT HYDRATED 2 FILTRATION MOLYBDENUM TRIOxIDE COMBINED SULFURIC ACID SOLVENT EXTRACTION SOLUTION CONTAINING RECOVERY OF ACID SOLUBLE METALSI MOLYBDENUM AND RHENIUM CU, ZN, FE, ETC.

RHENIUM To AMMONIUM SOLVENT EXTRACTION MOLYBDATE RECOVERY TO RE METAL PRODUCTION INVENTORS ELLSWORTH W DAUGHERTY ALBERT E. ERHARD JAMES L. DROBN/CK ATTORNEYS June 12, 1973 E w DAUGHERTY ET AL 3,739,057 PROCESS FOR THE RECOVERY OF RHENIUM AND MOLYBDENUM VALUES FROM MOLYBDENl-TE CONCENTRATE Filed July 9, 1971 2 Sheets-Sheet 2 INVENTORS ELLSWORTH W DAUGHERTY ALBERT E. ERHARD JAMES L. DROBN/CK ATTORNEYS United States Patent US. Cl. 423-50 16 Claims ABSTRACT OF THE DISCLOSURE Process for the recovery of molybdenum and rhenium from molybdenite which comprises: oxidizing the molybdenum in the molybdenite concentrate slurry to the hexavalent form with oxygen or oxygen-containing gases and less than a stoichiometric amount of nitric acid for the sulfide sulfur present, recovering molybdenum and rhenium values from the resulting solution when it contains up to 600 g./l. of sulfuric acid with an amine or quaternary ammonium type extractant, removing the molybdenum and rhenium values from the extractant with ammonium hydroxide, selectively recovering rhenium values from the resulting alkaline solution with a quaternary ammonium type extractant, recovering the remainder of the molybdenum values from the eluate, stripping rhenium from the extractant with perchloric acid or perchlorate salt and recovering rhenium from the stripping solution.

SUMMARY OF THE INVENTION Conventional processes for the recovery of molybdenum from molybdenite involve roasting the molybdenite concentrate in air or otherwise processing it at high temperatures with the consequent release to the atmosphere of polluting gases, such as oxides of sulfur. The molybdic oxide product produced by these processes requires extensive purification. In view of the stringent regulations now being promulgated by the states and federal government regulating the amounts of polluting gases, such as sulfur dioxide, which can be emitted to the atmosphere, processes for the recovery of metals from sulfide ores Without release of sulfur-containing gases are in demand. Another requirement for new processes is that they produce a higher purity molybdic oxide product.

Rhenium, which occurs largely in molybdenite, has now become a valuable metal for use in catalytic applications and others. Prior processes for the recovery of molybdenum from molybdenite have generally not been designed for the recovery of rhenium along with the molybdenum. Substantial recovery of rhenium along with molybdenum would enhance the commercial feasibility of any molybdenum recovery process.

Recovery of molybdenum as molybdic oxide from molybdenite concentrates using an oxidizing leach catalyzed by nitric acid is disclosed in the article entitled Oxidizing Leach of Sulfide Concentrates and Other Materials Catalyzed by Nitric Acid by C. Bjorling and G. A. Kolta, p. 135, of Result of Papers Published From the International Mineral Congress, Technical Papers, 7th Meeting, New York, NY. 1964, Published 1965. The application of the same type process to other nonferrous metals is disclosed in US. Pat. 2,805,936.

In accordance with the proces disclosed in the article, a relatively high concentration of nitric acid is required. Further, in order to perform the leaching necessary to recover 99% molybdic oxide as disclosed, it is necessary to at least partially neutralize the sulfuric acid formed in the oxidizing leach. The article also refers to performing the oxidizing leach in two steps.

Reduction of the amount of nitric acid used is an important economic consideration. Reduction of nitric acid is a saving in itself and it necessarily results in lesser amounts of nitrogen oxide gases being formed with less oxygen being required to oxidize these gases to prevent their release to the atmosphere and reform nitric acid.

Neutralization of the sulfuric acid formed in the oxidizing leach before recovery of dissolved molybdenum is time consuming and the neutralization agent adds to the expense of the process. Neutralization of the sulfuric acid eliminates the possibility of cost reduction through sale of the acid. Further, the presence of contaminant metals or metalloids complicates the recovery of molybdenum by leaching and makes it more difiicult to obtain a high purity product.

Although rhenium has been recovered from the flue gases resulting from the roasting of molybdenite as a calcined molybdic oxide product is recovered, no successful wet process for the simultaneous recovery of molybdenum and rhenium from molybdenite in substantial amounts is known. So far as is known, there are no oxidation leach processes utilizing nitric acid for the recovery of both molybdenum and rhenium from sulfide ores.

Accordingly, the principal object of this invention is to provide a process for the recovery in high yields of high purity molybdenum and rhenium from sulfide ores or concentrates by an oxidizing leach process utilizing nitric acid, which requires a minimum amount of nitric acid, eliminates the necessity for neutralizing the sulfuric acid formed during the oxidizing leach, and is effective in the presence of other metal or metalloid contaminants.

The process of the invention comprises subjecting finely divided molybdenite concentrate to an oxidizing leach in the presence of nitric acid to form insoluble molybdenum compounds and a solution having dissolved therein the rhenium values and some of the molybdenum values, recovering from the solution the molybdenum and rhenium values with an amine or quaternary ammonium type extractant, stripping molybdenum and rhenium values from the solvent with ammonium hydroxide, separating the rhenium from the molybdenum in the stripping solution with a quaternary ammonium type extractant, followed by final recovery of molybdenum and rhenium by conventional techniques.

It has been found that the process of this invention surprisingly requires about one-tenth the amount of nitric acid required in the prior process. By the use of an ion exchange system peculiarly applicable to the molybdenite oxidation leach solution for recovering molybdenum and rhenium values in the solution, the necessity of a further molybdenum recovery leaching step is avoided with consequent elimination of the necessity for neutralizing the sulfuric acid formed in the oxidation leach. This leaves the sulfuric acid available for sale. The extraction step recovers rhenium from this oxidation leach solution along with molybdenum. Further, the extraction step selectively recovers molybdenum and rhenium in the presence of the particular contaminant metals and metalloids present in the oxidation leach solution.

The process requires about 1025 grams of nitric acid per liter of solution in contrast to the prior process which required about grams per liter. The amount of nitric acid required is about A of the theoretical stoichiometric amount for the reaction involved in the oxidation leach step, i.e.:

MOS2+ H2MOO4 2H2SO4 Substantial recovery of the molybdenum and rhenium values in the oxidation leach solution has been effected by use of an amine type ion exchange resin in the presence of up to 600 grams of sulfuric acid per liter of solution. So far as is known, this has never been done at acid concentrations approaching those used in this process. The lower limit of the amount of sulfuric acid present is determined by the speed of the process necessary for economic feasibility. The process is most advantageously performed in an autoclave to prevent escape of gases and to effectively enable control of pressure and temperature. It was found that the process can be conducted within acceptable temperature and oxygen pressure ranges.

As to the particle size of the concentrate, a very small particle size is preferable to provide the maximum feasible contact surface area.

The sulfuric acid formed in the process can be marketed without processing the leach solution or it can be readily purified before marketing.

The process is readily performed within a period of one hour. Process time is an important economic consideration.

The principal contaminant metals are iron and copper. The amine type and quaternary ammonium ion exchange resins used selectively recover molybdenum and rhenium in the presence of these metals.

The amine type resins which are operative to extract molybdenum and rhenium values from the oxidation leach solution include conventional long chain primary, secondary and tertiary amines used in the industry as metal ion extractants. Quaternary ammonium compounds may also be used. A preferred amine is a tertiary amine with a mixture of C 43 carbon chains sold under the trade name of Alamine 336. Other preferred amines are those sold under the trade names Amberlite LA-l (secondary amine), Alamine 304 (tri-lauryl amine) and Amberlite XLA-3 (primary amine). These amines are of the type disclosed in US. Pats. 3,052,516 and 3,156,524 and are referred to herein as amine type resins or amine reagents. The quaternary ammonium extractants are operative for separating rhenium and molybdenum from the alkaline strip solution containing these metals as ammonium molybdate and ammonium perrhenate.

Conventional aromatic hydrocarbon diluents are used with the amine and quaternary ammonium resin extractants.

The quaternary ammonium extractants which are suitable are of the type disclosed in US. Pats. 3,083,085 and 3,575,687. A preferred agent is one being sold under the trade name of Aliquat 336.

The amine or quaternary ammonium extractant is highly effective to selectively extract rhenium and molybdenum from the oxidation leach solution which contains metal ion contaminants occurring in molybdenite. The solution also contains sulfates and nitrates among other salts resulting from the catalytic oxidation leach.

Some of the molybdenum from the molybdenite goes in solution during the oxidation leach step and the remainder is recovered mainly as an insoluble hydrated molybdic oxide, which is calcined to a high purity oxide.

The degree of conversion of the molybdenum to the insoluble compound, and consequently the amount to be recovered from solution by the extraction agent, can be controlled. The extraction step, or a second leach step accompanied by neutralization of sulfuric acid as in the prior art, is necessary to recover the molybdenum in solution. The extraction step is necessary to recover the rhenium from the oxidation leach solution. It is an obvious advantage of this invention, resulting in a reduction of required nitric acid, among other advantageous features, that the molybdenum in solution can be recovered in the extraction step necessary for the recovery of rhenium with an extractant peculiarly adaptable for this purpose to the nitric acid treated oxidation leach solution.

The oxidizing agent, nitric acid, can be supplied as aqueous nitric acid, nitrates, or by the addition of nitrous Oxide gases. whi h a e oxidized to n tr c acid du g the reaction. Oxygen is introduced into the autoclave under pressure as required. The autoclave used was of the conventional type equipped with pressure and temperatureindicating devices.

The process of the invention is outlined in FIG. 1 of the accompanying drawings depicting a flow diagram of the process.

In practicing the process of the invention, the molybdenite concentrate is introduced to the pressure reactor vessel as a wet slurry. Use of the wet slurry is an advantage of the present invention, since in the roasting processes the concentrate used must be dried. After the wet slurry is added to the reactor, water is added as necessary. The slurry may contain as high as 25% solids.

Nitric acid is then added to the slurry in the reactor in an amount varying from 0.037 to 0.37 pound of nitric acid per pound of molybdenum in the reactor, depending on the purity of the concentrate employed.

The temperature of the slurry containing the nitric acid is raised to about C. prior to introducing oxygen gas to the reactor. Oxygen is introduced to the reactor at varying pressures, a pressure of p.s.i.g. being used in a number of the examples. Oxygen-containing gases may be used.

The oxidation leach reaction produces an oxide of nitrogen in which the nitrogen has a lower valence than when introduced to the system, and thus the oxide is volatile and exists in the top of the reactor. The oxygen present will oxidize the nitrogen oxides back to nitric acid and the reaction proceeds as in the beginning. These reactions are proceeding simultaneously and the total molybdenite oxidation reaction is complete at times in no more than one hour, depending on the amount of molybdenite present in the system.

The pressure reactor is then discharged, substantially all of the rhenium being dissolved and at least 85% of the molybdenum values being present as an insoluble hydrated hexavalent molybdenum oxide compound.

After the solids and liquid have been separated, the solid hexavalent molybdenum oxide can either be dried and marketed or subjected to conventional ammonia dissolution techniques and finally recovered as ammonium molybdate or calcined to produce a high purity molybdenum trioxide.

The solution containing the rhenium values and less than 15% of the molybdenum values is subjected to solvent extraction with an amine type or quaternary ammonium solvent to separate the rhenium and molybdenum values from the sulfuric acid and other metal impurities, such as copper, zinc and iron. The molybdenum and rhenium barren sulfuric acid solution can be further processed for recovery of other metal values, such as copper, prior to utilization or discarding to waste.

The amine or quaternary ammonium extractant is diluted in either an aliphatic or aromatic hydrocarbon diluent and mixed with the strong sulfuric acid solution resulting from the oxidation leach step, with the result that the molybdenum and rhenium values are transferred to the solvent phase. These metal values are then re-extracted from the solvent phase by mixing with a strip solution containing ammonium hydroxide or other alkaline stripping agent, such as other alkaline hydroxides, carbonates, etc. The beneficial effects of staging in a countercurrent manner can be taken advantage of, if desired, to increase the yield.

The ammonia strip solution containing ammonium molybdate and ammonium perrhenate is further processed with a quaternary ammonium type extractant or solid ion exchange resin to separate the rhenium from the molybdenum, the rhenium reporting to the solvent phase. This procedure is disclosed in US. Bureau of Mines Report of Investigations 6246, 1963, by P. E. Churchward and J. B. Rosenbaum. The ammonium molybdate is recovered from the aqueous rhenium-barren phase using conventional techniques. Rhenium values are recovered from the solvent by stripping with perchloric acid or perchlorate salt followed by recovery of rhenium as ammonium perrhenate in accordance with conventional procedures.

It has been found that the rate of oxidation leach is much faster if heat of reaction is removed from the pressure vessel during the reaction. The removal of heat prevents pressure build-up which in turn prevents introduction of oxygen under the existing conditions. The net effect is that more oxygen is available for the oxidation of the oxides of nitrogen back to nitric acid and the oxidation of molybdenum to the insoluble hydrated molybdic oxide. Experimentation has shown that during the reaction there is a large temperature differential between the dome gases and the slurry in the bottom of the reactor with the latter being much lower, the high temperature of the dome gases being due to the exothermic oxidation of the nitrogen oxide gases to nitric acid. Accordingly, it is preferred to locate cooling elements in the top of the reactor to remove heat as fast as possible. To accomplish the favorable heat removal the specially designed reaction vessel of FIG. 2 of the drawings was constructed.

Referring to FIG. 2, the numeral indicates the wall of the pressure vessel which is provided with cooling jacket 12. The upper body of the vessel 10 terminates in a neck portion 14 terminating in a circular flange 16 defining the top opening of the vessel which is closed by the top 18 secured to flange -16 by bolts and nuts 20. A drain pipe 22 in the bottom of the vessel provided with valve 24 is for draining slurry from the vessel. The vessel is mounted on legs 25.

A neck 28 having a flange 30 with a top 32 bolted thereon by bolts and nuts 34 is seated in the top 18 of the vessel. A rotating mechanical seal 36 is mounted in top 32 and a turbine shroud 38 extends into the vessel 10 from the bottom of top 32 and is constructed integral therewith. The shroud is provided with gas inlet orifices 40 on opposite sides. The bottom of the shroud 38 terminates in a flat circular flange 42 which is provided with slurry inlet orifices 44. A motor 46 is mounted on the top 32 for driving turbine shaft 48 to rotate turbine blades 50.

A feed inlet pipe 52 provided with valve 54 is mounted in vessel top 18. A pressure gage 56 is also mounted in the top 18 for measuring the internal pressure of the vessel. -For removing heat from the upper section or dome of the reactor, cooling coils 60 are mounted in the dome section with inlet 62 and outlet 64 extending through the upper wall of the vessel 10. Similar coils 60' are shown schematically in the bottom of the vessel for removing heat from slurry. These coils are optional. They may be mounted with inlet and outlet pipes through the vessel wall-like coils 60 A thermowell 68 for liquid temperature and a thermowen 70 for gas phase temperatures are mounted in the vessel wall as shown with the former extending into the slurry area and the latter extending into the gas area.

During the entire period for the oxidation leach, cooling fluid is circulated through the coils and also the coils 60 if the latter are used. Other cooling means to remove heat from the reaction area may be used.

The following examples are illustrative of the invention but not limiting thereof. In the examples, percentages are given in weight percentages. Unless otherwise indicated the samples used in the examples had approximately the following composition:

Constituent: Wt. percent Mo 53.9-56.5 Re 0.08l-0.089 Cu 1.05-1.15 Fe 1.33-1.45

EXAMPLE 1 The purpose of this example was to illustrate the conversion of MoS to M00 in a typical nitric acid oxidation of molybdenite.

Four hundred grams of molybdenite concentrate was transferred to a pressure autoclave reactor to which 25 grams of nitric acid were added along with one liter of water. The apparatus was sealed and heated to 125 C. at which point oxygen was introduced to keep a pressure of 150 p.s.i.g. The temperature reached a maximum of 170 C. The oxidation of molybdenite was substantially complete in a period from l-2 hours and was complete in 4 hours. The results are given in Table 1.

TABLE 1 M0 in solution percent 8.8 Rein solution do 96.0 H 50 concentration of filtrate g./l 459 M08 conversion to M00 "percent" 99+ The results show that almost 100% conversion of MoS to M00 is obtained by the nitric acid oxidation process.

EXAMPLE 2 The purpose of this experiment was to determine the range of nitric acid necessary to dissolve rhenium values in molybdenite and oxidize the quadravalent molybdenum in molybdenite to the hexavalent form.

Various quantities of nitric acid were introduced into a pressure autoclave containing 100 grams of molybdenite concentrate and one liter of water. The entire contents were reacted for one hour at 170 C. and

p Fo llowing the reaction, the entire contents were filtered for solids and solution recovery with the solution being analyzed for Mo, Re, and Cu. The filter cake, believed to be a hydrated molybdenum oxide compound, was leached with an ammonia solution, followed by leaching with dilute hydrochloric acid to determine the amount of unreacted sulfide material remaining. The results are presented in Table 2.

TABLE 2.-EFFECT OF NITRIC ACID M082 to Cu in M0 in Re in H2804 con- M003 eon,

HNO3 added to system, solution, solution, solution, centration, version- 1b /1b M percent percent percent g./l. percen t The results show that about 0.037 wt. percent of nitric acid based on molybdenum is required to initiate the oxidation reaction, and that at about 0.371 wt. percent substantially all of the M08 has been converted to M00 EXAMPLE 3 The purpose of this example was to determine the eifect of sulfuric acid on bringing rhenium, molybdenum, and copper into solution during pressure oxidation of a molybdenite concentrate and on the conversion of MoS to M Sulfuric acid was added in measured amounts to the concentrate mixture as necessary to control the sulfuric acid concentration. The amount of nitric acid used was 0.21 pound of nitric acid per pound of molybdenum. The experiment was performed under conditions similar to those for Example 2. The results are reported in Table 3.

nium values from the solution obtained after filtering the slurry obtained by the molybdenite oxidation reaction described in the foregoing examples. The following solvents were used in this test. All were diluted in an aromatic hydrocarbon having a. flash point of 117 F.

5 volume percent Aliquat 336 (quaternary ammonium compound) TABLE 3.EFFECT OF SULFURIO ACID CONCENTRATION Cu in M0 in Rein H2804 con- M00: con- H2804 added to system, solution, solution, solution, centration, version, g./l. Mo percent percent percent g./l. percent The data in Table 3 indicate that the presence of sulfuric acid up to a concentration of 466 g./l. has very little effect on the conversion of M05 in molybdenite to M00 The presence of sulfuric acid has little or no effect on reducing rhenium to solution and only a slight efiect on molybdenum reduced to solution.

EXAMPLE 4 The purpose of this experiment was to determine the effect of oxygen overpressure on oxidation of MoS to M00 over a narrow temperature range. Various oxygen overpressures were used. The temperature varied between 100 to 110 C. The amount of nitric acid used was 0.28 pound per pound of quadravalent molybdenum to be oxidized and the reaction was allowed to proceed for one hour. The results are given in Table 4.

TABLE 4.EFFECT OF OXYGEN OVERPRESSURE Percent MoSz to Oxygen over- M0 in Be in M00; pressure, p.s.i.g. solution solution conversion The results of Table 4 indicate that the oxygen overpressure at the 100-110 C. operating temperature does not have any great eifect on the oxidation rate of the molybdenite. A small decrease in conversion rate can be noted as the oxygen overpressure is increased.

EXAMPLE 5 In order to determine the eifect of temperature on molybdenite oxidation, three experiments were performed on 100 gram samples of the concentrate. The nitric acid added to each system was 0.28 pound per pound of quadravalent molybdenum to be oxidized. A pressure of about 150 psi. was used. The reaction period at a given temperature was held constant at one hour. The results are presented in Table 5.

TABLE 5.-EFFECT OF TEMPERATURE Percent MoSz to Pressure, M0 in Be in M00: Temperature, C. p.s.i.g. solution solution conversion The results of Table 5 indicate that temperature does affect the reaction rate with a large increase in reaction rate occurring from 105 125 C.

EXAMPLE 6 The purpose of this experiment was to investigate various solvents for extraction of molybdenum and rhe- 5 volume percent Alamine 304 (tri lauryl amine) 5 volume percent Amberlite XLA-3( primary amine) The aqueous feed solution analyzed as follows:

All three reagents extracted some molybdenum and all of the rhenium values in a very short time from the strong sulfuric acid solution. Additional staging would have recovered more than 90% of the molybdenum values on the solvent.

EXAMPLE 7 Another extractant was investigated and involved a mixture of 5% Alamine 336 (a mixture of C and C carbon chains having a molecular weight of 392) and 95% Cyclosol 53 (an aromatic hydrocarbon having a flash point of 117 F.), which was mixed with the same solution used in Example 6 to determine the amount of molybdenum which could be extracted. The organic to aqueous phase ratios were varied. The retention time during mixing in separatory funnels was two minutes. The results are reported in Table 7.

TABLE 7.MOLYBDENUM EggIRAGTION USING ALAMINE 55 Aqueous phase analysis Mo after mixing, extracted, Phase ratio O/A g./1. Mo percent 25.5 24.9 it? ft 7. 17.8 47.8 10.1 70.5 7.8 77.1 6. 6 80.6 3.6 89.5

l The aqueous from the phase ratio of OIA=5 was mixed with fresh (in solvent.

EXAMPLE 8 This experiment was performed to investigate the range of sulfuric acid concentration within which suitable molybdenum and rhenium extraction can be made. The sulfuric acid concentration of the solution resulting from the oxidation step was adjusted with distilled water or concentrated sulfuric acid. Analysis of the solution indicated that 8.0 g./l. Mo and 0.05 g./l. Re were present in solution. The extractant used for this experiment con- 9 tained 4 volume percent Alamine 304, 5% tridecanol and 91% kerosene. The solvent to aqueous phase ratio was 4 and the phases were mixed for one minute before allowing them to disengage for separation and analysis. The results are reported in Table 8.

TABLE 8.-MOLYBDENUM AND RHENIUM EXTRACTION AS A FUNCTION OF SULFURIC ACID Percent rhenium and molybdenum extracted by the solvent Sulfuric acid concentration, g.l1. Re M0 EXAMPLE 9 This experiment was performed to investigate the effectiveness of an aliphatic hydrocarbon diluent with tertiary and secondary amine solvents when extracting molybdenum from the solution resulting from the oxidation process. The tertiary amine was the Alamine 336 used in the previous example. The concentration used was 10 volume percent in a kerosene having a flash point of 175 F. The secondary amine is marketed by Rohm and Haas Company under the name of Amberlite LA-l, has a molecular weight of 351 to 393 and is mixed with kerosene to result in a solvent containing 10 volume percent Amberlite LA-l. The feed liquor used for this experiment contained 14.58 g./l. Mo and 330 g./1. H 50 Several contacts were made at an organic to aqueous phase ratio of 1. The data is presented in Table 9.

TABLE 9.MOLYBDENUM EXTRACTION USING A SEC- The data indicate that greater than 90% of the molybdenum values can be extracted with the solvents employed as shown by the aqueous analysis following each contact.

EXAMPLE 10 This experiment was performed to investigate the effectiveness of the process of this invention on a pilot plant scale.

A 100-gallon autoclave reactor was charged with 83.0 pounds of molybdenite concentrate containing 67.2 pounds of M00 and 50 gallons of water. The rhenium content was 0.06% (0.0498 pound). The temperature of the slurry was raised to 310 F., and 2.2 pounds of nitric acid were added. Sufficient oxygen was added intermittently to keep the pressure at 140 p.s.i.g. Another 1.1 pounds of nitric acid were added at the end of 20, 40, 60, and 68 minutes of reaction time. Oxygen was fed to the system until the reaction was complete as indicated by the oxygen consumption, which was negligible at the end of 2.0 hours. The temperature measured in the top of the reactor never exceeded 380 F. The slurry was cooled to 200 F. at which time the reactor was discharged. Analysis of the solids and solution indicated that 99.8% of the quadravalent molybdenum had been oxidized to the hexavalent state.

Analysis of the solution after oxidation indicated the presence of 24.5 g./l. Mo and 0.118 g./l. Re. The H 50 concentration as determined by base titration to phenol phthalein end point was 247 g./l. H 50 The solution was fed to a continuous solvent extraction circuit were the molybdenum and rhenium values were separated from most of the sulfuric acid and metallic cations such as iron, copper, and zinc. An aqueous ammonia solution (5 N) was used to strip the metal values from the solvent to result in a solution containing 192 g./l. Mo and 0.855 g./l. Re. The solvent employed was 5% Alamine 336 and Cyclosol 53 diluent. The purified strip solution was further contacted with a solvent containing 5% quaternary ammonium compound (Aliquat 336) in 95% Cyclosol 53 diluent to separate the rhenium values from the molybdenum values. The rafiinate solution containing the molybdenum values was fed to a spray dryer to recover 15.2 pounds of M00 or 22.6% of the molybdenum introduced to the autoclave reactor. The solvent was stripped of its rhenium values using 1 M perchloric acid to result in a purified rhenium solution containing 97% of the rhenium values or 0.0483 pound of Re in the perchloric acid solution. The rhenium solution was further purified by conventional techniques to produce an ammonium perrhenate product of 99.9% purity.

The solid hydrated molybdenum oxide was leached with an ammonia solution to dissolve the molybdenum values as ammonium molybdate. The ammonia insoluble material was filtered and the ammonium molybdate solution spray dryed to produce a high purity molybdenum trioxide. Ammonium molybdate can be produced, if desired. 50.7 pounds of M00 were recovered during this step of the process, making a total of 65.9 pounds of M00 recovered by the oxidation and solvent extraction steps.

The process can be eflectively and economically conducted at temperatures from about 100 C.-200' C. at pressures up to about 300 p.s.i.g. and in a time of not more than about 1-2 hours.

The percentage of hexavalent molybdenum which is solubilized in the oxidation leach step can be controlled and it is believed that this percentage has a bearing on the amount of nitric acid used and the overall efliciency of the process. To convert the last 15-20 percent of molybdenum present to the insoluble hydrated molybdic oxide would probably require an unproportionate excess of nitric acid.

The invention provides a process by which substantially all of the molybdenum and rhenium values in molybdenite can be recovered in one overall operation. It has the advantage that dissolved rhenium and molybdenum 'values from the oxidation step can be simultaneously recovered in the presence of other metal impurities and large amounts of formed sulfuric acid by the quaternary ammonium or amine type solvent which is peculiarly applicable to the solution resulting from the nitric acid oxidation step. This eliminates the necessity for neutralization of the solvent which was necessary in prior processes for the recovery of dissolved molybdenum with a leaching step. The process has the further advantage that substantially all of the rhenium is dissolved in the oxidation leach step so that it can be recovered along with molybdenum.

What is claimed is:

1. A process for recovering molybdenum and rhenium values from molybdenite which comprises:

(a) introducing a water slurry of particulate molybdenite into a pressure vessel,

(b) introducing nitric acid into the pressure vessel to form a slurry with the molybdenite, in an amount from about 0.037-037 pound of nitric acid per pound of quadravalent molybdenum in the molybdenite to be oxidized to hexavalent molybdenum,

(c) raising the temperature of the slurry inside the pressure vessel to about 100 C. to start the reaction,

(d) introducing oxygen under pressure into the pressure vessel to provide an oxidizing medium with the nitric acid to oxidize the sulfides of molybdenum and rhenium to the oxides,

(e) maintaining the temperatuure within the gas phase reaction zone in the vessel as the oxidation proceeds at substantially that at which nitrogen oxide gases formed during the oxidation are oxidized to nitrogen dioxide for regeneration of nitric acid by the reaction of formed nitrogen dioxide with water,

(f) recovering the insoluble solid molybdic oxide formed by oxidation from the pressure vessel, and

(g) contacting the liquid component of the slurry containing up to 600 grams per liter of sulfuric acid with an extractant selected from the group consisting of an amine extractant and a quaternary ammonium extractant to recover dissolved molybdenum and rhenium values on the extractant.

2. The processing of claim 1 in which the temperature of the slurry varies from about 100 C.200 C., the pressure in the pressure vessel is maintained up to about 300 p.s.i.g., and vapor from the gas phase reaction zone is continuously circulated through the slurry to aid in temperature control of said zone.

3. A process for the recovery of molybdic oxide and rhendium from molybdenite which comprises:

(a) introducing a Water slurry of particulate molybdenite into a pressure vessel,

(b) introducing nitric acid into the pressure vessel in an amount from about 0.0370.37 pound per pound of molybdenum,

(c) raising the temperature of the slurry inside the pressure vessel to at least about 100 C. to start the reaction,

(d) introducing oxygen under pressure into the pressure vessel to provide an oxidizing medium with the nitric acid to oxidize the sulfides of molybdenum and rhenium to the oxides,

(e) removing heat from the gas phase reaction zone in the pressure vessel and continuously circulating vapor from the gas phase reaction zone through the slurry to maintain the temperature in the gas phase reaction zone as the oxidation proceeds to that at which nitrogen oxide gases formed during the oxidation are oxidized to nitrogen dioxide for regeneration of nitric acid by the reaction of nitrogen dioxide with water,

(f) recovering the solid molybdic oxide formed by oxidation form the pressure vessel, and

(g) contacting the liquid component of the slurry remaining in the pressure vessel and containing up to 600 grams per liter of sulfuric acid with an extractant selected from the group consisting of an amine extractant and a quaternary ammonium extractant to recover dissolved molybdenum and rhenium values on the extractant.

4. The process of claim 3 in which the slurry temperature inside the pressure vessel is maintained between about 100 C.-200 C. during oxidation and the pressure is maintained in the pressure vessel up to about 300 C.

5. A process for recovering molybdic oxide from molybdenite by oxidation of the molybdenite which comprises:

(a) introducing a water slurry of molybdenite particles into a pressure vessel and sealing the pressure vessel,

(b) introducing nitric acid and oxygen into the pressure vessel to oxidize the molybdenite,

(c) raising the temperature of the slurry in the pressure vessel as necessary to start oxidation of the molybdenite,

(d) continuing the introduction of nitric acid and oxygen into the pressure vessel as necessary as oxidation proceeds,

(e) maintaining the pressure vessel sealed until oxidation is substantially complete and containing within the pressure vessel all nitrogen oxide gases formed during the oxidation reactions occurring therein,

(f) controlling the temperature inside the pressure vessel to maintain the temperature of the gas phase reaction zone as oxidation proceeds at substantially that at which nitrogen oxide gases formed during the oxidation reactions are oxidized to nitrogen dioxide so that nitric acid is regenerated by the reaction of formed nitrogen dioxide with water in the pressure vessel and excessive pressure build-up in the pressure vessel is prevented to permit rapid introduction of oxygen to accelerate the oxidation reactions occurring within the pressure vessel; whereby molybdenum sulfide is rapidly oxidized to molybdic oxide and nitric acid is continuously regenerated in situ as the the oxidation reactions in the pressure vessel proceed, and

(g) recovering insoluble molybdic oxide from the slurry in the pressure 'vessel.

6. The process of claim 5 in which rhenium in the molybdenite is solubilized and the solubilized rhenium is recovered from the slurry in the pressure vessel.

7. The process of claim 6 in which some of the molybdenum in the molybdenite is solubilized and the solubilized molybdenum is recovered from the slurry in the pressure vessel.

8. The process of claim 5 in which the temperature inside the pressure vessel is controlled by removal of heat therefrom.

9. The process of claim 5 in which the temperature of the gas phase reaction zone is controlled by removal of heat from the interior of the pressure vessel as the oxidation reactions proceed and by continuous circulation of vapor from the gas phase reaction zone in the upper part of the pressure vessel through the slurry in the lower part of the pressure vessel.

10. The process of claim 5 in which the temperature of the slurry in the pressure vessel is maintained below about 200 C. as the oxidation reactions therein proceed.

11. The process of claim 5 performed within a time of about l-2 hours.

12. The process of claim 5 in which the amount of nitric acid introduced into the pressure vessel varies from about 0.037-0.37 pound of nitric acid per pound of quadravalent molybdenum in the molybdenite to be oxidized to hexavalent molybdenum.

13. A process for recovering molybdic oxide from molybdenite by oxidation of the molybdenite which comprises:

(a) introducing a water slurry of molybdenite particles into a pressure vessel and sealing the pressure vessel,

(b) introducing nitric acid and oxygen into the pressure vessel to oxidize the molybdenite,

(0) raising the temperature of the slurry in the pressure vessel as necessary to start oxidation of the molybdenite,

(d) continuing the introduction of nitric acid and oxygen into the pressure vessel as necessary as the oxidation proceeds,

(e) maintaining the pressure vessel sealed until oxidation is substantially complete and containing within the pressure vessel all nitrogen oxide gases formed during the oxidation reactions occurring therein,

(f) controlling the temperature inside the pressure vessel and thereby the pressure therein by removing l3 14 from the pressure vessel heat of reaction generated by References Cited the oxidation reactions occurring therein to prevent UNITED STATES PATENTS pressure build-up inside the pressure vessel and thereby permit rapid introduction of oxygen therein 3,453,277 7/1969 matzkl et a1 23 15 W to accelerate the oxidation reactions occurring inside 5 3,495,934 2/1970 Zlegenbalg et a1 23-22 the pressure vessel; whereby molybdenum sulfide is 1,118,150 11/1914 Robertson 23 15 W rapidly oxidized to insoluble molybdic oxide, and 3,656,888 4/1972 Barry et 23-15 W (g) recovering insoluble molybdic oxide from the slurry in the pressure vessel. OTHER ERENCES 14. The process of claim 13 in which gases from the 10 Bjorling et al., Result of Papers Published From the gas phase reaction zone in the pressure vessel are con- International Mineral Congress, Technical Papers, 7th

tinuously circulated through the slurry. Meeting, New York, NY. 1964, published 1965, pp.

15. The process of claim 13 in which rhenium and 127438.

molybdenum solubilized during the oxidation are Usataya, Chemical Abstracts, vol. 47, 1953, p. 5313d.

recovered from the slurry. 15

16. The process of claim 5 in which solubilized rheni- HERBERT CARTER, Prlmary EXamlner um and molybdenum are recovered from the slurry after oxidation 'by contacting the slurry with an amine extractant. 56 

